1. Field of the Invention
The present invention relates to a vulcanizing method and a vulcanizing apparatus of a tire capable of vulcanizing a tire at optimal temperature in accordance with various portions of the tire so as to enhance the performance of the tire.
2. Description of the Prior Art
In general, when a tire is vulcanized, as shown in FIG. 5, a vulcanizing apparatus having an outer mold (a) having a tire forming barrel (a1), and a bladder (b) for pushing a raw tire (t) against an inner peripheral surface of the tire forming barrel (a1) is used. A tire is heated from outside by heat transmitted from heaters (h) provided on upper and lower platen plates (c) through the outer mold (a). The tire is heated from inside by high temperature thermal pressure medium (e) charged in the bladder (b), and the outside and inside of the tire is controlled to be constant temperature.
On the other hand, characteristics required by various portions of the tire such as a tread portion, a side wall portion, and a bead portion are different. For example, the tread portion requires grip properties, wear resistance, crack resistance, low febriferous properties, and the like, so as to contact the ground to transmit the driving and braking forces. The side wall portion requires flexibility, crack resistance and weather resistance, so as to prevent the carcass from being injured, and so that the side wall portion can flexibly be bent. The bead portion requires rigidity, wear resistance and low febriferous properties so that the tire is fitted and fixed to the rim. Therefore, different compound rubbers are used for different portions of the tire for satisfying these individual requirements, and as the tire is sophisticated and the output becomes higher in recent years, the characteristics of the compound rubbers are enhanced.
In order to allow the individual compound rubbers to exhibit the individual characteristics sufficiently, it is necessary to vulcanize the individual compound rubbers at optimal vulcanizing temperatures.
However, in the conventional vulcanizing apparatus, since the outside and inside of the tire are controlled at constant temperature, it is difficult to sufficiently exploit the performance of the compound rubber, and the tire performance is deteriorated.
Especially in a steam vulcanizing method using saturated steam as the thermal pressure medium, or in a gas vulcanizing method using a thermal pressure medium which is a mixture of steam and inert gas such as nitrogen gas, steam condensed in vulcanization tends to be accumulated at a lower side (s2) as drain (d), or low temperature inert gas and high temperature steam tend to be separated upward and downward in the bladder (b). As a result, an uneven temperature is generated between an upper side (s1) and a lower side (s2) in the inner surface of the tire (t), which promotes the deterioration of the tire performance which prevents optimization of the vulcanization.
In Japanese Patent Publication JP-A-6-18699, it is proposed to change the temperature of the outer mold depending upon a portion of the tire (tread portion and side wall portion) so as to vulcanize the compound rubber at optimal vulcanizing temperature. However, the various portions of the tire are uniformly heated from inside through the bladder by thermal medium in the steam vulcanizing method or in the gas vulcanizing method, and uneven temperature is generated between the upper and lower sides (s1) and (s2) and therefore, it is difficult to sufficiently optimize the vulcanization.
Accordingly, it is an object of the present invention to provide a vulcanizing method and a vulcanizing apparatus capable of vulcanizing various portions of the tire under optimal temperature conditions without generating uneven temperature between upper and lower portions, and capable of optimally enhancing the tire performance.
To achieve the above objects, according to the vulcanizing method in a first aspect of the present invention, in the vulcanizing method for vulcanizing a tire by heating from an outer forming surface and an inner forming surface of a vulcanizing apparatus comprising an outer mold having the outer forming surface for forming an outer surface of the tire and an inner mold having the inner surface for forming an inner surface of the tire, the inner forming surface of the inner mold is divided into a plurality of inner forming surface portions in accordance with portions of the tire along an outline of a tire meridian cross section, and temperatures of the inner forming surface portions are varied to vulcanize each of the portions of the tire.
According to the vulcanizing method in a second aspect of the invention, the outer forming surface of the outer mold is divided into a plurality of outer forming surface portions in accordance with portions of the tire along the outline of the tire meridian cross section, and temperatures of the outer forming surface portions are varied to vulcanize each of the portions of the tire.
According to a vulcanizing apparatus in a third aspect of the invention, the vulcanizing apparatus of the tire comprises an outer mold having the outer forming surface for forming an outer surface of the tire and an inner mold having the inner surface for forming an inner surface of the tire, wherein the inner forming surface of the inner mold is divided into a plurality of inner forming surface portions in accordance with portions of the tire along the outline of the meridian cross section, and the inner mold is provided with heaters capable of heating the inner forming surface portions at different temperatures.
According to the vulcanizing apparatus in a fourth aspect of the invention, the outer forming surface of the outer mold is divided into a plurality of outer forming surface portions in accordance with portions of the tire along an outline of the tire meridian cross section, and the outer mold is provided with heaters capable of heating the outer forming surface portions at different temperatures.